Japanese Patent Application Publication No. 2005-5779 published on Jan. 6, 2005 discloses a semiconductor relay. For example, in the construction having no gate line (its third embodiment), the relay includes first and second signal terminals (output terminals), a substrate (a print board), first and second semiconductor switches (MOSFETs for output) and a control circuit (a charging and discharging control circuit). Hereinafter, this relay is referred to as a “prior art relay”.
The substrate includes first and second signal patterns (output lines) and a land (a source line) which are formed on a surface of the substrate. The first and second signal patterns are located between the first and second signal terminals so as to form a signal line. The control circuit includes a light receiving chip (a control IC) that is mounted on the land.
The first semiconductor switch is used to make or break the connection between the first signal pattern and the land. The second semiconductor switch is used to make or break the connection between the second signal pattern and the land. Specifically, the gates of the first and second semiconductor switches are mutually connected and also connected to the light receiving chip. The sources of the first and second semiconductor switches are mutually connected and also connected to the land (source line). The drains of the first and second semiconductor switches are connected to the first and second signal patterns, respectively. Therefore, the first and second semiconductor switches are turned on or off at the same time. When the first and second semiconductor switches are turned on, the first semiconductor switch makes the connection between the first signal pattern and the land, and the second semiconductor switch also makes the connection between the second signal pattern and the land. Thereby, the first and the second signal terminals are mutually connected.
However, in the prior art relay, there is an issue that the impedance matching of the circuit including the signal line is disturbed. That is, since the first and second signal terminals are mutually connected through the land, the land functions as a third signal pattern (a source line). Accordingly, all of the land becomes a stub with respect to the signal line (i.e., the first and second signal patterns).